Human Protein C is a vitamin-K dependent plasma protein which is involved in the control of blood coagulation and fibrinolysis. An expression system for the production of recombinant human protein C has been established. This system is based on mammalian cells in culture, stably transfected with a DNA construction expressing human Protein C. This expression system secretes into the culture media, approximately 400 ug/L of Protein C, which is gamma-carboxylated, completely processed to its two-chain form and capable of full biological activity. Methodologies, including random integration screening, gene amplification and dicistronic mRNA constructions will be used to increase the expression level of Protein C. Some innovative modifications will be made to the expression construction in order to produce Protein C molecules which are more efficiently processed, gamma-carboxylated or activated during secretion. The goal is to establish a development scale expression system in order to produce human Protein C for various therapeutic applications.